1. Field of the Invention
The present invention generally relates to a fuel-injected engine for an outboard motor. More particularly, the present invention relates to an improved fuel injection control system for a direct injection internal combustion engine used in a marine environment.
2. Related Art
Two cycle engines are widely used, particularly in applications where high specific outputs and relatively uncomplicated, simple engine constructions are desirable. Thus, two cycle engine are frequently employed as the power plant in a marine outboard motor because of the small space available in the powerhead of such engines and the demand for relatively high performance.
However, because of environmental concerns, there is a desire to significantly improve the performance of two cycle engines particularly in the area of exhaust emission control. One particularly advantageous method for reducing unburned hydrocarbons in the exhaust emissions without sacrificing engine performance is using direct cylinder injection.
It should be noted that, particularly in two-stroke applications, it is desirable to open and close the fuel injectors as rapidly as possible. The rapid opening and closely results in longer available injecting time. To accomplish this rapid opening and closing, the fuel injectors are provided with springs of sufficient stiffness to rapidly close the fuel injector while not causing a rebound opening upon closing. Accordingly, the increased spring stiffness requires a larger current to be circulated through a solenoid which controls opening and closing of the fuel injector.
If the engine speed increases, the fuel injector must be increasingly actuated or if the load on the engine increases, the actuation duration must be increased respectively. Either scenario results in increased energy sent to the transistor that controls the solenoid. The transistor, therefore, is susceptible to rapid increases in temperature over time. Accordingly, high-speed, high-load applications of direct cylinder injected engines or indirectly injected engines featuring certain configurations of injectors are subject to possible heat damage of the transistors.